Image forming apparatuses according to the related art, such as printers, copiers, and multi-functional peripherals that incorporate the functions thereof, which are capable of printing (forming) images on transfer materials, such as paper sheets, are known. In general, an image forming apparatus fixes toner images onto paper sheets using a fixing unit, including a heating rotating body (heating roller) having a heater and a pressurizing rotating body (pressurizing roller) rotating while being pressed against the heating rotating body, by heating and pressing the paper sheets onto which the toner images have been transferred.
After power is turned on or after being in a stop state (e.g., power saving mode) for a long time, when such an image forming apparatus invokes printing an image on a first paper sheet, the image forming apparatus does not print the image on the first paper sheet immediately and waits until the fixing unit is heated to a predetermined temperature (a warm-up temperature) to print an image on the first paper sheet. Immediately after turning on power or resuming operation, the entire image forming apparatus is cool and the temperature of the fixing unit is significantly low. Therefore, when images are to be printed in sequence on multiple paper sheets, the temperature of the fixing unit may be lower than the temperature required to fix the images. Accordingly, the warm-up temperature set for known image forming apparatuses is generally high to include a margin in consideration of the temperature of the apparatus to be significantly low immediately after the power is turned on or operation is resumed. As a result, the warm-up time for the known image forming apparatuses, which is the time required to heat the apparatus to the warm-up temperature, is long.
Various methods of shortening the warm-up time of an image forming apparatus have been proposed. For example, an image forming apparatus that can print an image (perform image formation) on the first paper sheet in a significantly short amount of time by shortening the warm-up time in accordance with the thickness of the paper sheet have been known.
However, with such an image forming apparatus, merely the amount of time required to print an image on the first paper sheet is reduced. Therefore, when images are to be printed in sequence on multiple paper sheets, the amount of time required for printing the images in sequence after turning on power or resuming operation cannot be reduced.